1. Field of the Invention
This invention relates to a guide tube for guiding the movement of an insertion tube of an industrial endoscope into a passageway of an object to be inspected.
2. Prior Art
In the case where a passageway of an object, such as a sewer, to be inspected by an industrial endoscope is turned at right angles or branched, it is difficult to insert an insertion tube of the endoscope into the passageway without any guide. The reason is that the insertion tube must have a sufficient rigidity not to be axially compressed easily so that it can be advanced along the passageway in response to a push, and therefore the insertion tube of such a rigidity is subjected to much resistance when passing through bent and branched portions of the passageway.
For this reason, a guide tube has heretofore been used for guiding the movement of the insertion tube of the endoscope into the passageway. The manner in which the insertion tube is inserted into the passageway with the aid of the guide tube will now be described with reference to FIGS. 13 to 15. The guide tube 60 is first inserted into a straight passageway 101 of an object 100 to be inspected, and then the insertion tube 51 of the endoscope 50 is inserted into the guide tube 60. The guide tube 60 is so flexible as to be bent but has such a rigidity as to withstand an axial compression. The passageway 101 is divided into branch passageways 101a and 101b at a T-shaped branch portion 102. The insertion tube 51 is advanced along the guide tube 60 until its front end 54 reaches the branch portion 102 beyond the front end of the guide tube 60. The endoscope 50 comprises a thumb nut 53 rotatably mounted on a body 52 and an operating wire (not shown) extending into the insertion tube 51 and operatively coupled to the thumb nut 53 and the front end 54. Upon rotation of the thumb nut 53, the front end 54 is bent via the operating wire. The front end 54 is bent toward the branch portion 101a by manipulating the thumb nut 53 as shown in FIG. 13. Then, as shown in FIG. 14, the guide tube 60 is pushed until its front end passes beyond the bent front end 54 of the insertion tube 51 and introduced into the branch passageway 101a. Then, as shown in FIG. 14, the insertion tube 51 is pushed until the front end 54 passes beyond the bent front end of the guide tube 60. At this time, since the front end of the guide tube 60 is bent, the insertion tube 51 can be smoothly advanced.
However, as described above, the guide tube 60 has a sufficient rigidity to withstand an axial compression, and besides its front end is not designed to be bent without any guide toward the direction in which the guide tube is to be advanced. Therefore, the guide tube 60 can not be passed through the branch portion 102 by itself. For this reason, it is necessary to first extend the front end 54 of the insertion tube 51 beyond the front end of the guide tube 60 at the branch portion 102 and then to bend the front end 54 to guide the guide tube 60 toward the branch 101a. This operation is cumbersome. In addition, when the guide tube 60 passes through the branch portion 102, it tends to scratch the outer surface of the bent front end 54 of the insertion tube 51 and the outer surface of that portion of the insertion tube 51 adjacent to the bent front end 54, thereby causing damage thereto.